This invention relates to a method and equipment for purifying lakes and marshes, and, more particularly, to technologies for purifying closed water areas, such as eutrophic lakes, marshes, dammed lakes, harbors, and the like, and especially, to technologies for purifying closed water areas serving as tap water sources or water areas in sight-seeing and recreation parks.
In recent years, many lakes and marshes have been polluted with eutrophic materials, such as nitrogen, phosphorus, and other similar materials which flow into them, particularly bodies of water which are closed and used as tap water sources. In those lakes and marshes, algae tends to grow quickly further accelerating such eutrophication, thereby polluting the water quality. So far, various technologies have been proposed for purifying those closed water areas. Those proposals can be classified into technologies for removing pollutants mechanically, technologies for activating microorganisms to treat the water, technologies for treating pollutants with chemicals, technologies for circulating part of the water for treatment in closed water areas, etc.
One of such prior art technologies, as disclosed in Japanese Patent Laid-Open No.95498/1990. relates to a method and equipment for treating eutrophic water in closed water areas. The method and equipment is provided with a process and equipment for removing algae growing thickly in eutrophic water; a process for treating water with an aerobic microorganisms; a process and equipment for treating water with aerobic microorganisms; and a process and equipment for removing residual phosphorus by chemical treatment.
Another prior art technology is disclosed in Japanese Patent Laid-Open No.287/1993. It relates to a purifier used for polluted water, wherein the purifier is provided with a bubble collecting raft provided with floats, each of which comprises top-recessed tubs arranged side by side at proper intervals, the tubs being connected to a catamaran frame on the water inside the catamaran frame so that each tub can be adjusted to a deep waterline; a bubble generator that generates bubbles from under the bubble collecting raft; and a bubble connecting means provided in each of the tubs for collecting bubbles coming into the tub, so that pollutants may be removed from the water in the target closed water area, such as a lake, marsh, sea, etc. to purify the water quality.
As eutrophication increases in closed water areas, such as lakes, marshes, dammed lakes, and the like, which are used as tap water sources or water parks, purifying facilities have also been reinforced with various purifying technologies. However, elements such as nitrogen, phosphorus, etc. that accelerate eutrophication in closed water areas are mainly supplied from rivers flowing into those water areas. The pollutants in the water from those rivers are diluted further in the water which is retained in closed water areas. Thus, a large amount of water must be treated when the above prior art is used. Furthermore, when the above prior art is used, the purifier manufacturing cost, the installation space, the driving energy, etc. is so large that the prior art has not been adopted in actual practice.